Question

Some part of journey of 555 km was completed by a car with speed
60 km/hr. Then the speed is increased by 15 km/hr and the journey is
completed. If it takes 8 hours to reach, find the time taken and distance
covered at the speed of 60 km/hr.​

Answer 1

Resposta:

First of all we write km/h

Ok.

We have 2 unknown distances and 2 unknown times:

1) x km at speed of 60km/h (time is A)

2) 555-x km at speed of 75km/h (time is B)

***If we sum 555-x + x we get 555km (total)

We know:

1)Total distance: 555km

2)A + B is 8h or A+B=8

So... We need to make another equation to solve for A and B.

Remember that time(t) is distance(d) divided by speed(v)

From $v=\frac{d}{t}$ becomes $t=\frac{d}{v}$

So...

$A=\frac{x}{60}$

or

$60A=x$

....

$B=\frac{(555-x)}{75}$

or

$75B=555-x\\x=555-75B$

...

now we have 2 equations x

So we can do

$60A=555-75B\\60A+75B=555$

Simplifying by 5 and by 3 we get:

$12A+ 15B=111\\4A+5B=37$

Now we solve the system for A and B (time)

$A+B=8\\4A+5B=37$

We get A=3 and B=5

Remember that A is 60km/h

So it was 3h at 60km/h

60*3=180

Time: 3h

Distance: 180km